The integration of various optical components on optical devices is now established in commercial practice. These integrated components provide functionality to the optical device that is typically intended to be utilized in conjunction with the intended use of the optical device. For example, wavelength tunable lasers may be integrated on an optical device with phase or amplitude modulators such as Mach-Zehnder interferometer modulators. Such lasers are also frequently integrated on the optical device with semiconductor optical amplifiers (SOA). Optical devices including these integrated components are particularly useful in connection with telecommunication applications.
The manufacture of these optical devices is very expensive, due much in part to the significant costs of the testing associated therewith. For example, one parameter that is measured during the testing of an optical device having an integrated wavelength tunable laser is wavelength. In the current state of the art, wavelength measurement is typically performed by optically coupling light emitted from one of the device facets into a suitable wavelength measurement system and therefore cannot be performed on-wafer. It is possible to use a grating out-coupler to extract light (vertically) from the device whilst it is still part of the wafer, but this requires careful optical alignment to collect the emitted light. Wavelength measurement is also sometimes required to be performed during use of the optical device, for example, to maintain a set transmission wavelength of a wavelength tunable laser.
Wavelength output from a laser is conventionally measured by such devices as an off-device wavelength meter instrument, a wavelength division multiplexer (WDM) coupler, or an etalon-type wavelength locker. Typically these methods cannot be performed at wafer level where the device facets have not yet been formed by means of cleaving the wafer into chips upon which the optical devices are formed and coating the exposed ends of the optical waveguides. Grating out-couplers do enable light to be emitted vertically from the device while the device is still part of the wafer, but again an off-device wavelength meter instrument is required for the actual wavelength measurement. Furthermore, instruments such as wavelength meters are slow and expensive. While the use of a WDM coupler is comparatively faster and less expensive, test results are less accurate and the use of bulky equipment is still required, and presently known methods for testing chips while in wafer form are difficult and impractical. Furthermore, an etalon-type wavelength locker is only capable of detecting changes in wavelength over a narrow wavelength range and does not provide test results in the form of absolute wavelength. Etalon-type wavelength lockers are installed at a very late stage on the product line (i.e., during the assembly of the device inside the packages), too late to be used cost effectively to discriminate good devices that provide the required wavelength coverage from those that do not.